Various processes for producing aldehyde and/or alcohol compounds by the reaction of a compound having at least one olefinic carbon-to-carbon bond with carbon monoxide and hydrogen in the presence of a catalyst are known. Typically, these reactions are performed at elevated temperatures and pressures. The aldehyde and alcohol compounds that are produced generally correspond to compounds obtained by the addition of a carbonyl or carbinol group, respectively, to an olefinically unsaturated carbon atom in the starting material with simultaneous saturation of the olefin bond. Isomerization of the olefin bond may take place to varying degrees under certain conditions; thus, as a consequence of this isomerization, a variety of products may be obtained. These processes are typically known as hydroformylation reactions and involve reactions which may be shown in the general case by the following equation:
            R      1        ⁢          R      2        ⁢    C    =                    CR        3            ⁢                        R          4                ⁢                              ⟶            catalyst                                CO            /                          H              2                                      ⁢                                  ⁢                                            and              ⁢                              /                            ⁢              or                                                                        R                  1                                ⁢                                  R                  2                                ⁢                C                            -                                                CR                  3                                ⁢                                  R                  4                                ⁢                CHO                                                                                        R                1                            ⁢                              R                2                            ⁢              C                        -                                          CR                3                            ⁢                              R                4                            ⁢                              CH                2                            ⁢              OH                                            +          isomers      ⁢                          ⁢      thereof      
In the above equation, each group R1 to R4 may independently represent an organic radical, for example a hydrocarbyl group, or a suitable atom such as a hydrogen or halogen atom, or a hydroxyl or alkoxy group. The above reaction may also be applied to a cycloaliphatic ring having an olefinic linkage, for example cyclohexene.
The catalyst employed in a hydroformylation reaction typically comprises a transition metal, such as cobalt, platinum, rhodium or ruthenium, in complex combination with carbon monoxide and ligand(s) such as an organophosphine.
Representative of the earlier hydroformylation methods which use transition metal catalysts having organophosphine ligands are described in U.S. Pat. No. 3,420,898, U.S. Pat. No. 3,501,515, U.S. Pat. No. 3,448,157, U.S. Pat. No. 3,440,291, U.S. Pat. No. 3,369,050 and U.S. Pat. No. 3,448,158.
In attempts to improve the efficiency of a hydroformylation process, attention has typically focussed on developing novel catalysts and novel processes for recovering and re-using the catalyst. In particular, novel catalysts have been developed which may exhibit improved stability at the required high reaction temperatures. Catalysts have also been developed which may permit the single-stage production of alcohols rather than a two-step procedure involving separate hydrogenation of the intermediate aldehyde. Moreover, homogeneous catalysts have been developed which may permit improved reaction rates whilst providing acceptable yields of the desired products.
Although organophosphine modified cobalt catalysts are known to be excellent catalysts in a single step hydroformylation reaction of olefinic compounds to alcohols, the use of such catalysts can also lead to the production of paraffins as a by-product. These paraffin by-products have very little commercial value. Also, in such reactions heavy organic materials (‘heavy ends’) may be produced as by-products. These by-products result in waste of reactants and require additional energy in order to separate them from the product stream. Further, in order to control the amount of heavy ends in the reactor system, they may be removed via a bleed stream. Such a bleed stream will also contain catalyst and product alcohol and/or aldehyde and will thus result in the loss of expensive catalyst and valuable products. It would therefore be desirable to reduce the amount of heavy ends and paraffin by-products formed in the hydroformylation process using organophosphine modified cobalt catalysts.
Furthermore, we have detected that cobalt catalysts comprising cobalt in complex combination with carbon monoxide and an organophosphine ligand may decompose during the reaction to produce solid cobalt deposits such as cobalt and cobalt carbide (a compound of cobalt and carbon, empirical formula CoyC, where y is in the range of from 2 to 3). Cobalt carbide is catalytically inactive in hydroformylation reactions. The presence of cobalt carbide also promotes further degradation of the cobalt catalyst, thereby resulting in an increased rate of catalyst usage. The cobalt carbide is not only catalytically inactive in hydroformylation reactions but also has a relatively bulky, porous structure and is insoluble in the reaction medium. This represents a significant disadvantage, particularly for homogeneous cobalt catalysts, because the cobalt carbide typically tends to agglomerate and form detrimental deposits on the internal surfaces of the production facility. The deposition of cobalt carbide impedes the running of a hydroformylation production facility with optimal efficiency. In particular, the deposition of cobalt carbide can cause plugging of the pipe work in the production facility, resulting in shut down of the production facility to allow for removal of these cobalt carbide deposits.
The present invention therefore seeks to provide a simple hydroformylation process which may be used in the one-pot conversion of olefinic compounds to alcohols, which not only reduces the amount of paraffin and heavy ends by-products produced, but also reduces the amount of cobalt catalyst lost through decomposition and formation of cobalt carbide and/or cobalt deposits on the internal surfaces of the production facility.
Additionally, since the demand for normal 1-alcohol products is greater than the demand for other alcohol products, it would also therefore be desirable to increase the proportion of normal 1-alcohols in the alcohol product composition.
U.S. Pat. No. 6,482,992 describes a process for the hydroformylation of olefins to give alcohols and/or aldehydes in a plurality of hydroformylation stages, each of which comprises: a) hydroformylating olefins having a carbon atom content of 6 to 24 carbon atoms in the presence of a cobalt- or rhodium catalyst in a reactor to the point of conversion of olefin reactant to product of 20 to 98%; b) removing the catalyst from the resulting liquid discharged from the reactor; c) separating the resulting liquid hydroformylation mixture into a low-boiler fraction comprising olefins and paraffins, and a bottoms fraction comprising aldehydes and/or alcohols; and d) reacting the olefins present in the low-boiler fraction in subsequent process stages comprising steps a, b and c and combining the bottoms fractions of process steps c) of all process stages. Different reaction conditions can be set in the hydroformylation reactors.
U.S. Pat. No. 5,112,519 describes a process for hydroformylation of olefins having the formula (C3)x, (C4)x or mixtures thereof, where x has the value of 1 to 10, using a catalyst with a phosphine ligand at a temperature sufficient to promote reaction while retarding paraffin formation. A hydroformylation process disclosed in U.S. Pat. No. 5,112,519 is conducted in a single reactor, wherein the hydroformylation temperature is held at 135° C. for 2 hours, followed by a reaction temperature of 160° C. for 48 hours (Example 2). The reason for the use of the initially lower temperature is stated as isomerising the double bond of the olefins to the chain end.
GB 1041101 describes a hydroformylation process carried out in the presence of an unmodified cobalt catalyst with a temperature gradient across the reaction system. An amount of water of less than 10% of the total reaction mass may be added to the reaction in order to decrease the production of by-products.
The addition of a similar amount of water, preferably in the latter stages of the reaction, is taught in U.S. Pat. No. 3,113,974, as a method of improving reaction yields.
WO 98/11468 describes the injection of water into the hydrofinishing stage of a multiple-step oxo-process for alcohol production, in order to reduce heavy by-products and to permit the use of a sulfur-tolerant catalyst during hydrogenation and/or hydrofinishing.
U.S. Pat. No. 4,401,834 is directed to a process for producing alcohols, wherein in a two-step oxo-process, water is added to the aldehyde-containing product of the hydroformylation step before it undergoes hydrogenation in order to break down any acetal by-products present in the reaction mixture.
Addition of water to a hydroformylation reaction is also described in GB 740708, which is directed to the preparation of aldehydes by hydroformylation of olefins, catalysed, at least in part, by an aqueous solution of cobalt acetate. At least a portion of said aqueous solution must be injected into the reactor system at a point where an appreciable share of the olefins have been converted to aldehydes, in order to prevent flooding of the reactor system and quenching of the reaction.
According to U.S. Pat. No. 2,809,220, the addition of water to the hydrogenation environment (i.e. after formation of aldehydes in a hydroformylation process), when using a sulfactive hydrogenation catalyst, leads to an increased yield of alcohols.
The continuous recycling of water, in an amount of up to 100 to 200 wt % based on the olefin in the feed, in the carbonylation, or aldehyde synthesis reaction mixture of an oxo-process, is taught in GB 703491 as beneficial for the recycle of the catalyst and also for reaction temperature control.
DE 2851515 teaches the use of from 2 to 5 wt % water in the reaction of olefins with hydrogen and carbon monoxide, wherein formic acid ester by-products formed in the reaction are fed back to the synthesis stage in order to be decomposed.